This invention relates to sampling valves and more particularly to a valve means and associated sample stream passageway that permits the safe sampling of process fluids through a conduit of a process stream under hazardous conditions while maintaining a fresh sample of the process fluids stream flowing through elements associated with the valve.
In process streams associated with fluid processes there is frequently a need for obtaining periodic samples of the process stream to provide the process operators with information for monitoring the productivity or progress of the process. In many such processes the process stream flowing through a conduit of the process is flowing under conditions that could be hazardous to personnel taking the sample; such hazards include high (or low) pressure, high temperature, extremely flammable or explosive streams, highly toxic streams, highly noxious streams, and many other possibly hazardous conditions. The taking of fluid samples of such process streams cannot usually be eliminated because of fear of the hazardous condition of the process stream, however the safety of the personnel taking the fluid sample should be of upmost concern to the process operators.
It is further a need that a fluid sample taken from a conduit of a process stream be truly representative of the condition of the process stream at the time that the fluid sample is taken. For that purpose, the taking of samples should be from a conduit of the process stream or a portion of the stream that is continuously in the process stream and therefore representative of the condition of the process stream at the time that the sample is taken. In some process stream sampling procedures, a sample is drawn from a portion of the process stream in a "one-way" sampling path. That is, the sample is drawn through some form of tubing not a conduit of the process stream and that sample is taken directly into the sample container. Some such sampling procedures require that a "flushing" portion of the sample pass through the "one-way" path to get to a "clean" sample of the stream. Such sampling procedures expose the sample taker to the hazardous conditions of the process which could include the high pressure or high velocity of the stream as the larger sample is wasted to get to the "clean" sample.
In other conventional sampling procedures or devices where there is not a continuous flow of the process stream in the sample passageway there may be a "dead" or "stale" volume of the process stream remaining in the passageways to the sampling device left from previous sampling procedures. That volume must be flushed or purged from the sampling device before the desired sample is taken if the sample is to be truly representative of the process conditions at the time of sample taking. While it may be the safest condition to stop the flow of the process stream during a sampling procedure, such an extreme condition would upset the process and cause productivity failures.
To avoid the foregoing, it is desirable that the taking of samples of a process stream be done with a sampling device that will eliminate or substantially reduce the exposure of the sample taker to any hazardous conditions, that will produce a sample that is truly representative of the process stream at the time that the sample is taken, and which sample taking will not interfere with the operation of a continuing process.